Sodium nitrate? Is that what is in that stuff?
I use an acid demand test to determine if it has the right amount. Keep the electrons from corroding the steel. Works good. Also keeps the fins in the flat plate heat exchangers from filling up.
Though, it seems that you could charge the OWB with an electric DC current and keep it from corroding, like they do the bridges here on the coast on highway 101. Might be cheaper just to go with the anti-corrosion stuff though. I have to drain my system here next month and recharge it with new anti-corrosion stuff that I got from the dealer. It has been 3 heating seasons now.